Robotic lawnmowers, autonomous lawn mowers, and self-propelled lawn mowers are currently available and are known in prior art. The current commercially available autonomous lawn mowers made by companies such as Belrobotics, Friendly Robotics, and Kyoda America use a continuous guide conductor boundary around the confined area. The autonomous lawn mowers randomly mowed around the confined area. This art is described in early patents such as U.S. Pat. Nos. 3,550,714 and 3,570,227 by Bellinger. More recently, Peless et al. U.S. Pat. Nos. 6,255,793 B1, 6,417,641 B2, 6,850,024 B2, and 7,155,309 B2 discusses this technology. These autonomous lawn mowers take time to mow the entire area completely and may miss certain sections of the lawn every operation. They require installation, excitation, and maintenance of conductor around the desired area. Also, Colens U.S. Pat. No. 6,321,515 B1 discloses a similar system where the buried wire restricts the mower to operate randomly within a certain area.
Some autonomous mowers use a pre-programmed or pre-recorded path for guidance such as Nokes U.S. Pat. No. 3,650,097, Geslinger U.S. Pat. No. 3,789,939, and Noonan et al. U.S. Pat. No. 5,204,814. These systems are unsatisfactory because of tire slippage, etc. Some RTK GPS-based systems have been developed and are outline in U.S. Pat. No. 5,956,250 by Gudat et al. These are very expensive systems and require open space areas. Trees blocking the signals may cause concerns.
Tracking the cut/uncut vegetation border has also been tried by various inventors. U.S. Pat. Nos. 3,425,197 and 3,924,387, both to Kita, uses electrical conductors touching the uncut grass. Martin U.S. Pat. No. 4,887,415 uses touch grass detection switches on the rear of the mower frame to provide an indication of the relative position of the cut/uncut grass boundary. The vehicle needs to be moving for the touch sensor to detect the boundary. U.S. Pat. No. 5,528,888 by Miyamoto et al. describes a plurality of mechanical rocking members to detect the cut/uncut boundary. The vehicle also requires to be moving in order to determine the boundary. Likewise, U.S. Pat. No. 6,255,793 B1 by Peless et al. discloses using mechanical plates attached to potentiometers spaced far apart to determine an estimated boundary. Similarly as Miyamoto et al., the autonomous vehicle needs to be moving in order to determine the boundary.
An optical tracking system to detect the cut/uncut grass boundary is described in Griffin U.S. Pat. No. 4,133,404. Griffin shows a fluorescent light source directed at the grass and the reflection from the grass is detected by a plurality of optical sensors. These optical sensors measure the intensity of the light after it has been reflected by the grass. The position of the cut/uncut grass boundary is determined by measuring a different reflected light intensity for the cut grass than for the uncut grass. However, if the light intensity differential between the cut and uncut grass is not significantly, the system does not work well. Yoshimura et al. U.S. Pat. No. 4,573,547 describes a system that uses photosensors to detect cut/uncut boundary by the presence or absence of the grass. Since the width of the grass blade is small, the optical sensor does not reliably detect the cross sectional grass blade and the cut/uncut boundary. To overcome this limitation, the photosensor is integrated with an orientation sensor. U.S. Pat. No. 4,777,785 from Rafaels discusses a plurality of optical sensors to detect the presence or absence of grass. Like the Yoshimura et al. patent, since the width of grass blade is small, the optical sensor does not reliable detect the cross sectional grass blade and the cut/uncut boundary. The patent description describes ways of improving the situation. Also, the system requires a reference path to be mowed prior to start of process.
The prior art does not reliably detect the boundary between the cut/uncut vegetation or provide a reasonable cost system for autonomously mowing a field.